The present invention relates to a connecting part for an ignition device for an internal combustion engine.
More particularly, it relates to a connecting part for incorporation into a cylinder head of an internal combustion engine.
Connecting parts of the above-mentioned general type are known in the art. In particular a connection part is known which is formed as a spark plug in view of its utilization and has a high voltage switching element formed as a trigger diode supplying voltage to the spark plug. This high voltage switching element switches from an electrically blocking to an electrically conducting condition in a jump-like fashion with the trigger voltage supplied to the ignition coil of the ignition device and supplies the subsequent spark plugs with a voltage jump. Therefore it substantially eliminates the effect of shunting at the spark plugs, which makes difficult the formation of the ignition spark at the electrodes of the spark plugs.
It is known that the voltage jump released by the high voltage switching element reaches the ignition voltage required for forming the ignition sparks at the plug electrode. The voltage jump is a partial voltage of the trigger voltage which structurally depends on the design of the high voltage switching element. The trigger voltage is smaller than the output voltage of the ignition coil by a voltage loss.
If the energy flow from the ignition coil to the spark plug corresponding to the ignition device is considered, the voltage loss which is produced due to the capacity distribution in the ignition device, depending on the location of the high voltage switching element, increases with the increase of the sum of the preceding and the subsequent capacity with respect to the preceding capacity. For compensating the voltage loss, the high voltage switching element must be designed for a corresponding higher trigger voltage than the ignition voltage in order to reach a predetermined average ignition voltage. Therefore, a very high initial voltage must be provided at the ignition coil. The high voltage is however connected with a reliability risk, since undesirable capacitative ground discharges can occur with electrode erosion at the spark plugs. In addition, the high voltage switching element and the ignition coil must be high voltage resistant, which leads to an increased price of these elements